Signaling system



y 1936- F. PREISACH 2,041,147

SIGNALING SYSTEM Filed Sept. 13, 1932 2 Sheets-:Sheet 1 8 FIG.

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as Hg EH5 Hg -/0Hs o o .1 .2 .3 I4 .5 .6 .1 .a .9 no H 5 so Ibo 150 200250M osnsrsa INVENTOR F. PRE/SACH ATTORNEY y 1936- F. PREISACH 2,041,147

S IGNALING SYSTEM Filed Sept. 13, 1932 2 Sheets-Sheet 2 FIG. 4A

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.2 .a 4 s @o :1 I000 05125150 FIG] lNVEN TOR F. PRE/SACH yak M ATTORNEYUNITED STATES PATENT OFFICE SIGNALING SYSTEM Franz Preisach,Bcrlin-Charlottenburg, Germany, assignor to Siemens and HalskeAktiengesellschalt, Berlin, Germany, a company of Germany ApplicationSeptember 13, 1932, Serial No. 632,959 In Germany September 25, 1931 9Claims. (01. 178-45) The present invention relates to signaling systemsand more particularly to magnetic materials and electromagnetic devicesemployed in such systems.

Among the more desirable properties of magnetic materials which are tobe used in signaling systems are high permeability at low magnetizingforces, and for a wide range of field intensities, low hysteresis loss,low coercive force and a high flux density for a given magnetizingforce. There is a great need and an important field of usefulness formaterials combining these properties in electromagnetic devices such astransformers, loading coils, relays, electro-acoustic devices,continuously loaded conductors etc. The desirable characteristicsmentioned presuppose a steep magnetization curve and at the same timethe absence of irreversible phenomena. It has been found in practicethat the very materials which have a steep magnetization curve have astrong tendency to irreversible phenomena such as the Barkhausen efiect.

An object of this invention is to so condition electromagnetic devicescomprising magnetic materials having high initial permeability toinhibit irreversible phenomena.

A further object of this invention is to reduce hysteresis losses andincrease the constancy of permeability of magnetic materials.

Another object of this invention is to improve the desirable propertiesof magnetic materials forming a part of signaling systems.

Another object of this invention is to treat strain-sensitive magneticmaterials to render their desirable properties immune to the eiiect ofmechanical strains such as pressure.

Among the magnetic materials which are par ticularly suitable fortreatments and applications in accordance with this invention are thosewhich reach the saturation point when subjected to small magnetizingforces and to high values of flux density for a given magnetizing force,i. e., those having a hysteresis loop of an approximately rectangularshape. A material of this type, for example, is found in an iron nickelalloy of about 78% nickel and the balance ironpossibly with smalladmixtures preferably of silicon. This composition exhibits in additionto a high initial permeability and arectangular shape of its hysteresisloop, a low coercive force.

In pursuance of the above mentioned objects,

this invention contemplates the reduction of 1 hysteresis loss ofmagnetic materials while at the or during their use in a signalingsystem where they are under the effect of an alternating or fluctuatingmagnetizing force, to an additional unidirectional magnetization, thelatter magnetization being applied in a direction substantiallyperpendicular with respect to the alternating magnetization, and beingfurthermore of such an intensity as to at least completely saturate thematerial.

The present invention has its' origin in the concept and discovery thatthe irreversible phenomena and consequently the hysteresis phenomena,which are causedby the abrupt change of the magnetic elementary domains,may be prevented if the magnetization changes are solely accomplished bycircular or rotary magnetic effects, i. e., magnetization by spacialrotation of the H-vector. Scientific investigations have shown that withcircular magnetization the hysteresis loss, as a function of the fluxdensity B, exhibits a maximum but becomes vanishingly small if theinduction is sufficiently increased. In a similar manner, thehysteresis-angle qb, that is the angle between H and B as a function ofB passes through a maximum and vanishes for the saturation value ofinduction.

Whereas it is old to subject magnetic materials to both alternatingcurrent and unidirectional cross magnetizations, whereby the hysteresisloss is reduced, the reduction of the hysteresis losses accomplishedthereby is not sufficient to compensate for the resulting decrease inthe alternating current permeability. In this invention, however, byhaving the unidirectional components of the magnetizing force ofsuii'icient magnitude to at least saturate the magnetic material and bydirecting it at right angles to the alternating components of themagnetizing force, the hysteresis loss due to the alternating componentsponding reduction in the alternating induction In some cases it hasbeen found that the mere combination of direct current and alternatingcurrent magnetizations and increase of the former to the saturationvalue 01' the materials renders the resulting circuits and devicesinoperative;- see, for example, page 188 of Principles of RadioCommunication by J. H. Morecorft, second edition, 1927. In these cases,it should be noted that the magnetizing forces are applied in the samedirection instead of perpendicular to each other as in this invention.

The invention will now be described in more detail with reference to theaccompanying drawings in which:

Figs. 1 and 5 represent hysteresis loops and vector diagrams used forgraphically depicting relations to be established between physicalproperties of materials treated in accordance with this invention;

Figs. 2 and 3 show permeability curves of materials treated inaccordance with the invention; and

Figs. 4, 4--A, 6, 'l and 8 schematically illustrate various practicalembodiments of the invention.

Hereinafter the alternating current magnetizing field will be designatedby Hw and the unidirectional or direct current field will be designatedH9. H8 is that intensity of the field at which the material has apractically vanishing hysteresis angle q: for a rotating magnetization.This occurs for a field H =Hs and an inductance B=B8, where the materialis practically in the saturation field for ordinary magnetization. Inother words, with ordinary magnetization oi H Hs no further perceptibleirreversible processes take place which are apt to cause losses. Thereversible rise B-Bs=f(H) is disregarded in the following, since thedifferential permeability ad which determines this value is small withrespect to is, assuming the B-vector corresponding to rotary Imagnetization to coincide with the direction of the H-vector (see thediagrams of Fig. 1) then we obtain with a direct current crossmagnetization exceeding the saturation point, a value for thealternating current permeability:

A valuable feature of this invention is found in the fact that for manymaterials such as high permeability alloys as is very high, andtheoretically may be higher than 0. Another feature of this inventionwhich is of considerable practical importance is found in the fact thatthe direct current magnetization entails practically no seriousreduction of the permeability. Thus for a magnetization -Hv=Hs at Hn=Hsthe permeability for small alternating fields is only 30% less than thevalue of the permeability in the absence of a direct current crossfield.

It may be emphasized that the requiremento'f a high s which is ofimportance from the standpoint of practical application is notnecessarily identical with the requirement of a high initialpermeability or a low coercive force. It is more a question of obtainingthe reversible saturation field with the smallest possible fieldintensity and the greatest possible inductance. It is also conceivablethat a material with low initial permeability and great coercive forcehas a greater as if the loop is sufficiently rectangular (in order toreach its saturation point soon after H becomes equal to Hc) and thesaturation value of the flux density is high. For this reason, ironnickel a1- loys, particularly those of the permalloy type are suitablefor the purposes of this invention. With permalloy, for example, it ispossible, at least theoretically, to obtain a direct currentpermeability #9 of 10,000 at a direct current magnetizing force of Hg of0.5 gauss. From a practical standpoint the facts may be slightlydifferent, which is partly due to unavoidable inhomogeneities of thefields, particularly of the cross field. This has the eiiect, that (1)Es may not be reached; (2) Hs is not perpendicular to Hw, consequentlyhysteresis occurs in many fields; (3) the field Hg is partly greaterthan calculated and the resulting permeability is somewhat lower. Thereduction of the hysteresis loss depends practically entirely upon theattainment of a homogeneous cross field. In practical embodiments anyinhomogeneities will have the effect that a desired constancy ofpermeability or hysteresis factor is obtained with a greater directcurrent cross field and a lower permeability than calculated.

We shall now consider in what manner the alternating currentpermeability curves of Fig. 2 depend upon the direct current crossmagnetization. The hysteresis loop shown in Fig. 1 may be taken as thebasis of the curves. It is found that with a direct current crossmagnetization 1;

tion magnetization, then this dependency becomes very low. With a crossmagnetization field .intensity of ten times the saturation magnetizationno variation of the permeability as a function of the alternating fieldis perceptible. The

I curves of Fig. 2 show that with increasing cross magnetization theinitial permeability decreases with respect to the value of thesaturation permeability. In practical embodiments of the invention, theintensity of the direct current cross magnetization to be applied willthus be determined by' the values of permeability and con- I stancy ofpermeability which are desired.

Fig. 3 shows curves depicting the variations of the permeability as afunction of increasing alternating magnetizing forces for a materialcomprising '78% nickel, a small amount of silicon 'and the rest iron.Curve 1: shows that when employing'a fdirect current cross magnetizationthe permeability remains somewhat in the order of magnitude of theinitial permeability (7500). Curve b shows that when the direct currentcross magnetization is increased, the permeability decreases, but theconstancy of permeability increases. "For the experiments a laminatedstrip of 0.15 mm. thickness and 35 mm. width was rolled together into atube, which, as shown in Fig. 4, was provided with a magnetizing windingtor the useful field. The tube was subjected to a unidirectional fieldin the direction of the tube axis, which was applied by means of a yokecarrying a winding traversed by direct current in a manner shown inFigs. 4 and 4A. Fig. 4 shows a yoke I0 whose shanks are magnetized bythe winding W which is traversed by direct current. In the yokeis'placed a tube of magnetic material H shown in more detail in Fig.4-A; it comprises the alternating current magnetization winding M and awinding. B for connection to a ballistic galvanometer for testingpurposes. By means of the direct current source G the unidirectionalfield generated by the direct current magnetization winding W may be setat a certain value and the alternating current field applied by thewinding M may be varied by varying the resistance R; in this manner thecurves of Fig. 3 were obtained. While the curve 0 was obtained withoutdirect current cross magnetization, the cross magnetizationcorresponding to the curve a lay in the saturation field while thatcorresponding to curve I) was increased considerably beyond thesaturation field.

Fig. 5 shows a set of hysteresis loops which were obtained from an Ironwire 1 millimeter in diameter and 40 centimeters long whileit wassubjected to different values of a circular direct current magneticfield. The wire was connected to a source of direct current so thatdirect current flowed through the wire from one end to the other andproduced a circular magnetic field within the wire in a manner similarto that described in article 70 on page 199 and illustrated in Fig. 96on page 201 of the first edition of Principles' of ElectricalEngineering by W. H. Timbie and V. Bush, published by John Wiley andSon, Inc. The wire was also surrounded by a coil which was employed tomeasure the magnetic characteristics of this wire in an alternatingcurrent magnetic field. The magnetic field due to the measuringalternating current in the coil is in an axial direction in the wire andthus at right angles to the circular direct current magnetic field. Fig.7 shows a similar arrangement applied to a group of wires for subjectingthem to a direct current magnetic field at right angles to thealternating current magnetic field. Curve a shows the hysteresis curveobtained without any current (i=0 A.) flowing in the wire. For curve b adirect current of 1.34 A. (;i.=1.34 A.) was flowing through the wireduring the time at which measurements were made. This direct currentcaused a circular magnetic field within the wire which is at rightangles to the alternating current magnetic field due to the coilsurrounding the iron wire. For curves c and d the direct current flowingthrough the iron wire was 3.1 A. (:i=3.1 A.) and 5.7 A. (5:57 A.)respectively. It is thus apparent that the hysteresis loop becomesnarrower and straighter as the direct current through the wire increasesand produces a stronger cross-magnetic field. This indicates that thehysteresis loss is materially decreased and the constancy of thepermeability increased by the rect current magnetic field at rightangles to the alternating current magnetic field.

Various embodiments and practical modes of application of the inventionwill now be briefly described.

The device shown in Fig. 4 may be adapted to satisfy the demands ofpractical installations simply by reducing the dimensions of the'yokeand of the magnetization windings. In many cases a permanent magnet maybe substituted for the windings W of Fig. 4. An arrangement showing apermanent magnet I3 is shown schematically in Fig. 6.'

The cross magnetization may also be produced by constructing themagnetic core in the form of wire bundles, each wire of the bundle beingtraversed by a direct current which generates a circular cross field inthe wire; see Fig. '7.

In the construction of toroidal loading coils and transformer coils, aninsulated iron wire may be coiled to form a toroidal core to which thewinding is then applied. A direct' current is applied to the two ends ofthe iron wire forming the core. Several iron wires of the same core orof different cores may be supplied in parallel with the direct current.Such arrangements are particularly suitable for telephone oraudio-transformers, distortionless coils, coils for filters and othernetworks, loading coils etc. Loading coils thus constructed areparticularly valuable in cases wherehigh current intensities areinvolved, for example, at the terminals of submarine cables. In such 7cable systems the magnetizing direct current may means well known insuperposed telephony and telegraphy. In the case of multi-eonductorcables, for example, a conductor or twin-conductor may be employed forthe direct current supply to the loading coils.

In the'case of continuously loaded cables the direct current crossmagnetization may be produced by providing a special spiralled conductoraround the loaded conductor or conductors, the cable armor being used asthe return conductor.

Fig. 8 schematically illustrates a submarine current through the loadingtape 6|, without departing from the spirit and scope of the invention.

An important advantage of thisinvention is found in the fact thatmagnetic materials treated as described above are rendered substantiallyimmune to external influences such as pressure for example.

What is claimed is:

1. A signaling system including an electromagnetic device whichcomprises a magnetic material, and means including a source of directcurrent and a source of alternating current for subjecting said materialto a unidirectional magnetizing force sufiicient tosaturate saidmaterial and to an alternating magnetizing force which has a directionperpendicular to the unidirectional magnetizing force.

2. A system as defined in claim 1, characterized in that the magneticmamrial has a hysteresis loop of substantially rectangular shape.

3. A system as defined in claim 1, characterized in that means isprovided for producing the unidirectional magnetization which includes ayoke, a direct current winding thereon and further characterized in thatthe material has the form of The cable a magnetic core magnetized in itslongitudinal direction by alternating load currents.

4. A system as defined in claim 1, characterized in that the magneticmaterial is constituted by wires which are traversed by a directcurrent.

5. A system as defined in claim 1 comprising a continuously loadedconductor, characterized in that the direct current magnetizing meansincludes a winding for generating a magnetic field preponderantly in thedirection of the conductor.

6. The method of treating a magnetic material during use which comprisessubjecting the material to the eflects or unidirectional and alternatingmagnetizing forces applied at right angles to one another, theunidirectional magnetizing force being of such a magnitude as tosaturate said material.

7. A communication cable comprising a core conductor for transmittingsignal currents, a loading material surrounding said conductor and anauxiliary conductor surrounding said loaded core conductor fortransmitting a n0n-signaling continuous current which produces a steadymagnetic field within said loading material which is substantially atright angles to the magnetic field due to signaling currents in saidcore conductor.

8. A signaling system including an electromagnetic device whichcomprises a magnetic material, a permanent magnet for producing aunidirectional steady magnetic field within said magnetic material whichsubstantially saturates said material, and means for subjecting saidmaterial to an alternating current magnetizing force which has adirection substantially perpendicular to the direction of saidunidirectional magnetic field.

9. In an electrical device, a magnetic body and means for simultaneouslysubjecting said body to a constant unidirectional magnetic field ofsuiilcient magnitude to substantially saturate said body and analternating current magnetic field which is directed at an angle to saidconstant magnetic field.

FRANZ PREISACH.

